Method and device for determining the compression factor of powders

ABSTRACT

A method to determine the compression factor of powders for processing by roller presses with a roller diameter of 100-400 mm. A rotating press-roller ( 2 ), a matrix ( 4 ) and a piston ( 11 ) for measurement of the compression factor are used in the inventive method. The device to carry out the inventive method consists of a rotating press-roller ( 2 ) which is connected to a groove ( 5 ) in a displaceable matrix ( 4 ) and a piston ( 11 ) connected to a ruler ( 17 ) and a pointer ( 15 ) by means of a guide element ( 12 ) and a guide rod ( 13 ), whereby the depth of the groove is greater than the 20° angle tangent on the press-roller ( 2 ) when measured from the horizontal center axis.

The invention relates to a method for determining the compression factorof powders for processing by means of roller presses having rollerdiameters of 100 to 400 mm.

Roller presses serve for pressing powders so as to form scabbed stripswhich are subsequently comminuted into granulate (EP-A-0 525 135). Thisprocess is referred to as the dry granulation method. The pressing ofthe powder takes place between 2 mutually opposed rollers, and,depending on the manufacturer, both rollers are mounted fixedly, that isto say have a fixed roller nip, or one of the two rollers is designed tobe movable, is subjected to hydraulic force and has a variable rollernip.

All roller presses have at least 2 press rollers and, depending on themanufacturer, are offered with various roller dimensions. The rollersare fed with powder either by means of gravity or with the assistance ofa filling worm.

The dry granulation method enjoys a special status in economic terms inthe pharmaceutical industry for the production of granulate, instead ofthe known wet granulation method.

In the initial phase of development of a new drug, it has been necessaryhitherto to dispense with development aimed at dry granulation as themost cost-effective production method, because the powder quantitiesrequired for a test are not available or are too costly. Most rollerpresses also lack appropriate instrumentation for obtaining useful datafor the intended development.

A suitable device is known according to EP-A-0 525 135. This devicedelivers reproducible results even with powder quantities as low as 100ml.

In the first development phase, only substantially smaller quantities(for example, 10 ml) are available for tests. The subsequent productionmethod must be defined as early as at this stage.

Tablets or capsules can be produced from granulate manufactured by knownmethods. The most important technological properties, such as thetypical entering angle and, resulting from this, the possiblecompression factor of the powder and also the product quantity per unittime, cannot be ascertained by tabletting.

The object of the invention is to provide a method for testing a powderfor its suitability for the production of granulate by the dry granulatemethod with roller presses on an industrial scale.

A further object is to make available a device for carrying out themethod.

The object is achieved, according to the invention, in that a rotatingpress roller, a die and a piston are used for measuring the compressionfactor.

In accordance with the present invention, a method of determining acompression factor of powders for processing by a roller presses havingroller diameters of 100 to 400 mm is proposed, which comprises the stepsof filling a groove of a die with powder, introducing a piston into thegroove, pushing the die on a rotating press roller until it touches aroller surface, opening an end of the die located opposite to the pressroller and pushing the die downward on the press roller until the powderrests on the roller surface, during a measurement exerting a force onthe piston for compressing the powder, and using a position of thepiston in relation to the roller for measuring a compression factor.

The advantage of the method according to the invention is that, by meansof a single press roller, in combination with a die for very smallpowder quantities, it is possible for the first time to havepredetermination for dry granulation on roller presses of all types. Itmakes it possible, with the least possible outlay in terms of material,to obtain the important data for a reliable prediction as regards thedry granulation method with roller presses and to keep the powderquantity required for a test as small as possible.

By the second roller being simulated, the quantity required wasbasically halved. Since the filling worm was dispensed with, a narrowpress roller could be selected. So that the measurement can be carriedout for all current roller presses of different designs, the deviceaccording to the invention has different measuring systems.

It proved particularly advantageous to compress a powder introduced in agroove in a nip predefined therein.

It is expedient to compress the powder introduced in the groove with apredefined force.

It is particularly advantageous for the groove to be formed in adisplaceable die. As a result of this arrangement, a second press rollercan be dispensed with.

It is expedient to move a piston provided in the groove via a guide partand a guide rod and to read off, from a rule and a pointer, a travelwhich represents a measured value.

The resulting press force is measured in the case of a permanentlypredefined roller nip.

The resulting roller nip is measured in the case of a permanentlypredefined press force.

In the device, the rotating press roller is assigned a groove in adisplaceable die and a piston via a guide part and a guide rod, a ruleand a pointer. The advantage of this is that only a single press rolleris required, with the result that the device is very simple. This deviceis suitable for determining the compression factor of powders,irrespective of the origin of a roller press.

On roller presses, because the press rollers are arranged in pairs, thetypical entering angle is active in each case on the left and on theright roller, but is required only once for assessment.

The unit of measurement for the highest press force exertedinstantaneously on the powder is: kN/cm of linear roller width. Thisforce is applied at a theoretical line transversely to the roller at thelocation where the two rollers are nearest. So that as little powder aspossible is required, this method employs rollers with a width of 1 cm.Wider rollers may also be used for comparative measurements, such as,for example, for scale-up validation.

So that behavior can be tested in the case of different rollerdiameters, the abutment may be mounted in different positions, so thatpress roller diameters of 100 to 400 mm from the various manufacturerscan be simulated.

The invention will be described in more detail by means of a drawing inwhich:

FIG. 1 shows the device according to the invention in cross section formeasurement in the case of a defined roller nip and the resulting pressforce

FIG. 2 shows a variant of the device according to the invention formeasurement in the case of a defined press force and the resultingroller nip.

In FIG. 1, a bearing block is designated by the reference symbol 1.Located in the bearing block 1 is the motor-driven drive shaft whichcannot be seen and on which an exchangeable press roller 2 is mounted.An abutment 3 capable of being mounted in different positions islikewise mounted, as a stationary carrier for a sliding surface 10 ofvariable thickness, on the bearing block 1. A die 4 is provided with agroove 5 which is wider than the width the press roller 2. The depth ofthe groove 5 is greater than a 20 degree angle tangent to the pressroller, as measured from the horizontal center axis. A transverse slide6 running tangentially to the roller surface seals off the die 4downward and prevents the powder from flowing out undesirably prior tomeasurement. The groove 5 is covered with a longitudinal slide 7. A stop8 is set in its vertical position on the clamping piece 9. A piston 11seals off the groove 5 upward. A guide part 12 prevents the piston 11from tilting in the groove 5. A guide part 12 and a piston 11 aremounted on the guide rod 13. A tared weight 14 having a permanentlyinstalled pointer 15 is mounted at the upper end of the guide rod 13. Aholder 16 stabilizes the guide rod 13 in its vertical position. A scale17 makes it possible to read off the respective position of the pistonbefore and after the process and to evaluate this position for thecalculation. Travel measurement may also be carried out electronicallyor optically. A load cell 18 is mounted between the back of the abutment3 and a retention means 19.

In FIG. 2, the method is simulated by roller presses which are providedwith a permanently defined press force and a variable roller nip. Inthis variant of the device, the displacement of the abutment 3 relativeto the press roller is additionally indicated and read off on a scale 21via a pointer 20. Travel measurement may also be carried outelectronically or optically.

In each version, the device may be arranged at an angle of between 0 and90 degrees out of the horizontal axis, so that all customary rollertypes can be simulated.

2 methods are customary for the measurement.

Measuring Method 1:

Either loosely dumped powder, that is to say the basis is the dumpingvolume of a powder or of a powder mixture, may be tested for compactingbehavior or, according to

Measuring Method 2

The die together with the loosely dumped powder or powder mixture can beprecompressed on a calibrated tamping volumenometer at 1250 strokesaccording to an acknowledged method for determining the tamping volume.

During operation, for filling, the die 4 is laid horizontally onto aclean suitable base. The groove 5 opened upward is filled with powder.

After the powder has been introduced into the groove 5 of the die 4, thetransverse slide 6 and the longitudinal slide 7 are pushed into theirguides and the piston 11 is introduced. As a result of the introductionof the transverse slide 6, of the longitudinal slide 7 and of the piston11, the powder space is closed. The die 4 is raised and pushed towardthe press roller 2, until the transverse slide 6 touches the rollersurface and the die comes to bear, on its rear closed side, against theabutment 3. The transverse slide 6 is then removed and the die 4 ispushed downward toward the press roller 2 until the powder comes to bearagainst the roller surface. The stop 8 of the longitudinal slide 7 willsimultaneously come to bear on the support 9. At this moment, theposition of the pointer 15 against the scale 17 is tared and the zeropoint is thus set.

Definition of the Measuring Operation:

If the travel covered on the circumference of the forward-rotating pressroller 2 is equal to the travel of the downward-moving die 4 and of thepiston 11, this means that the entire powder quantity introduced hasbeen compressed.

Roller nip=1 mm

The formula: $\frac{5}{1} \cdot \frac{100}{100 + 0}$

yields a compression factor=5

The entering angle can be read off from a table.

A differential value between the travel of the piston 11 and that on thecircumference of the press roller 2, which is equal to the travel of thedie 4 is obtained when the powder, because of its changed enteringbehavior, allows a lower entering angle and therefore causes a recoilvalue on the piston 11. This recoil value is indicated and read off onthe rule 17 via the piston 11, the guide rod 13 and the pointer 15. Therecoil value is added to the travel of the die in order to calculate thecompression factor.

The following formula is obtained, for example

Roller travel on the circumference 100 mm Die travel 100 mm + pistonrelative to the die = 50 mm Groove filling depth = 5 mm Roller nip = 1mm

The formula $\frac{5}{1} \cdot \frac{100}{100 + 50}$

yields a compression factor=3.333

The entering angle can then be read off from a table.

In this case, not all the powder entered the groove 5 and wascompressed, but, instead, only the powder which was within the range ofa smaller entering angle.

During the measuring operation, the force exerted on the load cell 18and the applied torque on the drive shaft of the press roller 2 arerecorded simultaneously.

The pressed powder strip removed from the die can then be furtherprocessed into granulate and be pressed to form one or more tablets orbe filled into capsules. Alternatively, the powder strip may be drilledin a separate, standardized tablet drilling appliance at variouslocations according to a defined method. The values obtained, via acomparative table, give information on the tensile strength of thepowder strip, this, in turn, being comparable to a corresponding tablethardness.

So that the behavior can be tested in the case of a defined press forceand the resulting roller nip, the abutment 3 is mounted on a linearguide 18.

The motor-driven drive shaft, which cannot be seen and on which theexchangeable press roller 2 is mounted, is located in the bearing block1. A hydraulic cylinder 19, capable of being mounted in variouspositions, is mounted, as a moveable carrier for the abutment 3 and thesliding surface 10, on the bearing block 1. The linear guides 18,likewise capable of being mounted in various positions, stabilize theabutment 3 in relation to the press roller axis. The die 4 is providedwith a groove 5 which is wider than the press roller 2. The depth of thegroove 5 is greater than a 20 degree angle tangent to the press roller,as measured from the horizontal center axis. A transverse slide 6running tangentially to the roller surface seals off the die 4 andprevents the powder from flowing out undesirably prior to measurement.The groove 5 is covered with a longitudinal slide 7. A stop 8 is set inits vertical position on the clamping piece 9. A piston 11 seals off thegroove 5 upward. A guide part 12 prevents the piston 11 from tilting inthe groove 5. The guide part 12 and the piston 11 are mounted on theguide rod 13. A tared weight 14 having a permanently installed pointer15 is mounted at the upper end of the guide rod 13. A holder 16stabilizes the guide rod 13 in its vertical position. A scale 17 makesit possible to read off the respective position of the piston before andafter the process and to evaluate this position for the calculation.Travel measurement may also be carried out electronically or optically.The hydraulic cylinder 19 is subjected to a defined pressure, and theapplied force acting on the abutment is calculated from the sum,pressure x area of the hydraulic cylinder. So that the powder can becompacted, the force applied by the hydraulic cylinder must be overcomeduring entry and the abutment 3 must be displaced in the linear guides.The value by which the abutment 3 is displaced is transmitted to thescale 21 via the rule 20 and is read off as the thickness of the pressedpowder.

2 methods are customary for the measurement.

Measuring Method 1:

Either loosely dumped powder, that is to say the basis is the dumpingvolume of a powder or of a powder mixture, may be tested for thecompacting behavior or, according to measuring method 2, the dietogether with the loosely dumped powder or powder mixture may beprecompressed on a calibrated tamping volumenometer at 1250 strokesaccording to an acknowledged method for determining the tamping volume.

For filling, the die 4 is laid horizontally onto a clean suitable base.The groove 5 opened upward is filled with powder. After the powder hasbeen introduced into the groove 5 of the die 4, the transverse slide 6and the longitudinal slide 7 are pushed into their guides and the piston11 is introduced. As a result of the introduction of the transverseslide 6, of the longitudinal slide 7 and of the piston 11, the powderspace is closed. The die 4 is raised and pushed toward the press roller2 until the transverse slide 6 touches the roller surface and the die 4comes to bear on its rear closed side against the abutment 3. Thetransverse slide 6 is then removed and the die 4 is pushed downwardtoward the press roller 2 until the powder comes to bear against theroller surface. The stop 8 of the longitudinal slide 7 willsimultaneously rest on the support 9. At this moment, the position ofthe pointer 15 against the scale 17 is tared and the zero point is thusset. The hydraulic cylinder is pressurized with a defined pressure via apump which is not shown.

The indication on the rule 21 is set at 0 against the pointer 20 and istared. Travel measurement may also be carried out electronically oroptically.

According to FIG. 2, the travel covered on the circumference of theforward-rotating press roller 2 is equal to the travel of the moving die4 and the piston 11. This means that the entire powder quantityintroduced has been compressed.

Groove filling depth=5 mm

Indication of roller nip on the rule (21) 1 mm

Groove filling depth = 5 mm Indication of roller nip 1 mm on the rule(21)

$\frac{5}{1} \cdot \frac{100}{100 + 0}$

yields a compression factor=5

The entering angle can then be read off from a table.

The applied press force KN/cm lin. was predefined as a fixed quantityand can be transmitted directly to production machines.

A differential value between the travel of the piston 11 and that on thecircumference of the press roller 2, which is equal to the travel of thedie 4, is obtained when the powder, because of its changed enteringbehavior, allows a lower entering angle and therefore causes a recoilvalue on the piston 11. This recoil value is indicated and read off onthe rule 17 via the piston 11, the guide rod 13 and the pointer 15. Therecoil value is added to the travel of the die in order to calculate thecompression factor.

The following formula is obtained, for example

Roller travel on the circumference 100 mm Die travel 100 mm + pistonrelative top the die = 50 mm Groove filling depth = 5 mm Roller nip = 1mm

The formula $\frac{5}{1} \cdot \frac{100}{100 + 50}$

yields a compression factor=3.333

In this case, not all the powder entered the groove (5) and was;compressed, but, instead, only the powder which was located within therange of a smaller entering angle. The applied press force KN/cm lin.was predetermined as a fixed quantity, and the travel covered by theabutment 3 can be read off on the rule 21 as a resulting nip width.

The applied torque yields a value which can be transmitted directly toproduction machines when the effective width of the press rollers in cmis multiplied by the measured value. It is more expedient, however, forthis value, too, to be defined in Nm/cm of roller width.

The pressed powder strip removed from the die can then be furtherprocessed into granulate and be pressed to form one or more tablets orbe filled into capsules.

What is claimed is:
 1. A method of determining a compression factor ofpowders for processing by roller presses having roller diameters of 100to 400 mm, comprising the steps of filling a groove of a die withpowder; introducing a piston into the groove; pushing the die on arotating press roller until it touches a roller surface; opening an endof the die located opposite to the press roller and pushing the diedownward on the press roller until the powder rests on the rollersurface; during a measurement exerting a force on the piston forcompressing the powder; and using a position of the piston in relationto the roller for measuring a compression factor.
 2. A method as definedin claim 1, and further comprising a step of compressing the powderfilled into the groove in a predetermined gap by the rotating pressroller.
 3. A method as defined in claim 1, and further comprisingcompressing the powder filled into the groove by the rotating pressroller with a predetermined force.
 4. A method as defined in claim 1,and further comprising providing the groove in the die which isdisplaceable.
 5. A method as defined in claim 1, and further comprisingmoving the piston provided in the groove by a guide part and a guiderod, and indicating a traveled distance on a ruler and a pointer.
 6. Amethod as defined in claim 1, and further comprising moving a hydrauliccylinder which is connected with an abutment, over two linear guides,and indicating a traveled distance on a ruler and a pointer.
 7. A methodas defined in claim 1, and further comprising fixedly presetting aroller gap, and measuring a resulting force.
 8. A method as defined inclaim 1, and further comprising fixedly presetting a pressure force, andmeasuring a resulting gap width.
 9. A device for determining acompression factor of powders for processing by roller presses havingroller diameters of 100 to 400 mm, the device comprising a die with agroove to be filled with powder; a piston introducable into the groove;a rotating press roller onto which the die is pushed until it touches aroller surface, the die having an end located opposite to the pressroller and openable, so that the die is pushed downward on the pressroller until the powder rests on the roller surface; means which duringa measurement exert a force on the piston for compressing the powder;and means using a position of the piston in relation to the roller formeasuring a compression factor.
 10. A device as defined in claim 9,wherein said die is displacable relative to said rotating press roller;and further comprising a ruler and a pointer; and a guide part and aguide rod connecting said piston with said ruler and said pointer.
 11. Adevice as defined in claim 10, and further comprising an abutment whichis fastened on two linear guides and connected with said roller and saidpointer.
 12. A device as defined in claim 9, wherein said groove has adepth which is greater than a 20 degree angle tangent to said pressroller, measured from a horizontal central axis.